U.S. patent number 7,707,880 [Application Number 12/031,976] was granted by the patent office on 2010-05-04 for monitoring method and system for determining rack airflow rate and rack power consumption.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Levi A. Campbell, Richard C. Chu, Michael J. Ellsworth, Jr., Madhusudan K. Iyengar, Robert E. Simons.
United States Patent |
7,707,880 |
Campbell , et al. |
May 4, 2010 |
Monitoring method and system for determining rack airflow rate and
rack power consumption
Abstract
Monitoring method and system are provided for dynamically
determining rack airflow rate and rack power consumption employing
a heat exchanger disposed at an air outlet side of the electronics
rack. The method includes: sensing air temperature at the air
outlet side of the electronics rack, sensing coolant temperature at
a coolant inlet and coolant temperature at a coolant outlet of the
heat exchanger, and determining airflow rate through the
electronics rack; and outputting the determined airflow rate
through the electronics rack. The determining employs the sensed
air temperature at the air outlet side of the rack and the sensed
coolant temperatures at the coolant inlet and outlet of the heat
exchanger. In one embodiment, the heat exchanger is an air-to-air
heat exchanger, and in another embodiment, the heat exchanger is an
air-to-liquid heat exchanger.
Inventors: |
Campbell; Levi A.
(Poughkeepsie, NY), Chu; Richard C. (Hopewell Junction,
NY), Ellsworth, Jr.; Michael J. (Lagrangeville, NY),
Iyengar; Madhusudan K. (Woodstock, NY), Simons; Robert
E. (Poughkeepsie, NY) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
40953863 |
Appl.
No.: |
12/031,976 |
Filed: |
February 15, 2008 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20090205416 A1 |
Aug 20, 2009 |
|
Current U.S.
Class: |
73/202.5 |
Current CPC
Class: |
G01F
25/0007 (20130101); G01F 1/34 (20130101); H05K
7/20836 (20130101); G01F 1/68 (20130101) |
Current International
Class: |
G01F
1/68 (20060101) |
Field of
Search: |
;73/202.5 ;361/695,727
;62/180 ;165/80.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Thompson; Jewel
Attorney, Agent or Firm: Monteleone, Esq.; Geraldine
Radigan, Esq.; Kevin P. Heslin Rothenberg Farley & Mesiti
P.C.
Claims
What is claimed is:
1. A method of monitoring an electronics rack comprising a heat
exchange assembly disposed at an air outlet side thereof, the
method comprising: sensing air temperature at the air outlet side
of the electronics rack; sensing coolant temperature at a coolant
inlet to the heat exchanger and coolant temperature at a coolant
outlet of the heat exchanger; determining airflow rate through the
electronics rack, the determining employing the sensed air
temperature at the air outlet side of the electronics rack and the
sensed coolant temperature at the coolant inlet and outlet of the
heat exchange assembly, wherein a known percentage of air egressing
from the electronics rack passes through the heat exchange
assembly; and outputting the determined airflow rate through the
electronics rack.
2. The method of claim 1, wherein sensing air temperature at the
air outlet side of the electronics rack comprises sensing air
temperature between the air outlet side of the electronics rack and
the heat exchange assembly at a plurality of locations and
averaging the sensed temperatures at the plurality of location to
obtained the sensed air temperature at the air outlet side of the
electronics rack.
3. The method of claim 1, wherein the determining comprises
determining the airflow rate through the electronics rack employing
in part a difference between the sensed coolant temperatures at the
coolant outlet and coolant inlet of the heat exchange assembly
(.DELTA.T.sub.sense).
4. The method of claim 1, wherein the heat exchange assembly
comprises an air-to-air heat exchanger, and wherein the method
further comprises determining effectiveness of the air-to-air heat
exchanger employing a difference between the sensed coolant
temperatures at the coolant outlet and coolant inlet of the
air-to-air heat exchanger (.DELTA.T.sub.sense), and a difference
between the sensed air temperature at the air outlet side of the
electronics rack and the sensed coolant temperature at the coolant
inlet of the air-to-air heat exchanger (.DELTA.T.sub.inlet), and
wherein the determining comprises determining airflow rate through
the electronics rack employing the determined effectiveness of the
air-to-air heat exchanger.
5. The method of claim 4, further comprising pre-calibrating the
air-to-air heat exchanger to correlate .DELTA.T.sub.sense and
.DELTA.T.sub.inlet to effectiveness of the heat exchanger for one
or more coolant flow rates through the heat exchanger, and wherein
the method further comprises obtaining coolant flow rate through
the heat exchanger and employing coolant flow rate through the heat
exchanger and effectiveness of the heat exchanger in determining
airflow rate through the heat exchanger and hence through the
electronics rack.
6. The method of claim 4, wherein the method further comprises
periodically, automatically performing the sensing air temperature,
the sensing coolant temperature, the determining and the
outputting.
7. The method of claim 4, wherein effectiveness (.epsilon.) of the
heat exchanger is defined as:
.DELTA..times..times..DELTA..times..times. ##EQU00001## and wherein
employing effectiveness of the heat exchanger in determining
airflow rate through the electronics rack includes determining
coolant flow rate through heat exchanger, wherein for the
determined coolant flow rate through the heat exchanger, airflow
rate through the heat exchanger is defined as:
CFM=e.sup.[(.epsilon.+A)/B] where A and B are constants obtained by
pre-calibrating the heat exchanger for the determined coolant flow
rate through the heat exchanger.
8. The method of claim 7, further comprising sensing air
temperature at the air inlet side of the electronics rack, and
wherein the determining further comprises determining power being
consumed at the electronics rack by determining capacity rate
(C.sub.r) of the electronics rack airflow as a product of airflow
rate through the electronics rack, mass density of the airflow
through the electronics rack, and mass specific heat of the airflow
through the electronics rack, and using the capacity rate (C.sub.r)
of the rack airflow to determine rack power by multiplying the
capacity rate (C.sub.r) of the electronics rack airflow by a
difference between air temperatures at the air inlet and air outlet
sides of the electronics rack (.DELTA.T.sub.rack).
9. The method of claim 8, further comprising sensing air
temperature at a plurality of locations at the air inlet side of
the electronics rack and averaging the sensed temperatures at the
plurality of locations at the air inlet side to obtain the air
temperature at the air inlet side of the electronics rack, and
sensing air temperature at a plurality of locations at the air
outlet side of the electronics rack and averaging the sensed
temperatures at the plurality of locations at the air outlet side
of the electronics rack to obtain the sensed air temperature at the
air outlet side of the electronics rack.
10. The method of claim 1, wherein the heat exchange assembly
comprises an air-to-liquid heat exchanger, and wherein the method
further comprises: sensing coolant pressure at the coolant inlet to
the heat exchanger and coolant pressure at the coolant outlet of
the heat exchanger; sensing air temperature at an air outlet side
of the heat exchanger (T.sub.ro2), and wherein sensing air
temperature at the air outlet side of the electronics rack
comprises sensing air temperature between the air outlet side of
the electronics rack and the heat exchanger (T.sub.ro); determining
capacity rate (C.sub.r) of air flowing across the heat exchanger
employing coolant mass flow rate through the heat exchanger, and a
difference between the sensed coolant temperatures at the coolant
outlet and coolant inlet of the heat exchanger
(.DELTA.T.sub.sense), and a difference between the sensed air
temperatures at the air outlet and air inlet sides of the heat
exchanger (.DELTA.T.sub.RDHX); and employing capacity rate of air
flowing across the heat exchanger in determining the airflow rate
though the electronics rack or power being consumed at the
electronics rack.
11. The method of claim 10, further comprising determining the
coolant mass flow rate through the air-to-liquid heat exchanger
employing a difference between the sensed coolant pressure at the
coolant inlet to the heat exchanger (P.sub.si) and the sensed
coolant pressure at the coolant outlet of the heat exchanger
(P.sub.so), and by pre-calibrating the air-to-liquid heat
exchanger, wherein the mass flow rate (m.sub.s) of coolant through
the heat exchanger is defined as: m.sub.s=[.DELTA.P/D].sup.G
wherein D and G are constants obtained by pre-calibrating the heat
exchanger for a determined coolant flow rate through the heat
exchanger.
12. The method of claim 10, wherein sensing air temperature at the
air inlet side of the heat exchanger (T.sub.ro) comprises sensing
air temperature at a plurality of locations at the air inlet side
of the heat exchanger and averaging the sensed air inlet
temperatures to obtain the air temperature at the air inlet side of
the heat exchanger, and wherein sensing air temperature at the air
outlet side of the heat exchanger (T.sub.ro2) comprises sensing air
temperature at a plurality of locations at the air outlet side of
the heat exchanger and averaging the sensed air outlet temperatures
to obtain the sensed air temperature at the air outlet side of the
heat exchanger, and wherein the method further comprises waiting a
defined interval before automatically repeating the determining of
at least one of airflow rate through the electronics rack or power
being consumed at the electronics rack.
13. The method of claim 10, further comprising sensing air
temperature at the air inlet side of the electronics rack, and the
determining comprises determining power being consumed at the
electronics rack by employing the determined capacity rate
(C.sub.r) of airflow through the heat exchanger and a difference
between the sensed air temperature at the air outlet side of the
electronics rack and the sensed air temperature at the air inlet
side of the electronics rack (.DELTA.T.sub.rack).
14. The method of claim 13, wherein capacity rate (C.sub.r) of air
flowing through the heat exchanger is determined as:
C.sub.r=(C.sub.s.times..DELTA.T.sub.sense/.DELTA.T.sub.RDHX) where
C.sub.s is the coolant capacity rate through the air-to-liquid heat
exchanger, and wherein the coolant capacity rate is determined as:
C.sub.s=m.sub.s.times.C.sub.pw.times..rho..sub.w where:
m.sub.s=coolant mass flow rate through the air-to-liquid heat
exchanger; C.sub.pw=coolant specific heat for a given coolant
temperature; and .rho..sub.w=coolant mass density.
15. The method of claim 13, wherein the determining comprises
determining airflow rate through the electronics rack and power
being consumed at the electronics rack, the determining airflow
rate through the electronics rack comprising:
CFM=2118.9.times.C.sub.r/(C.sub.p.times..rho.) where C.sub.p is the
coolant specific heat and .rho. is the coolant mass density, and
wherein determining power being consumed at the electronics rack
comprises: rack power=C.sub.r.times..DELTA.T.sub.rack.
16. A monitoring system for an electronics rack, the monitoring
system comprising: a heat exchange assembly disposed at an air
outlet side of the electronics rack; at least one temperature
sensor disposed at the air outlet side of the electronics rack
between the electronics rack and the heat exchange assembly; a
coolant temperature sensor disposed at a coolant inlet to the heat
exchange assembly and a coolant temperature sensor disposed at a
coolant outlet of the heat exchange assembly; and a control unit
coupled to the temperature sensors for obtaining sensed temperature
values and for employing the sensed temperature values in
dynamically determining and outputting airflow rate through the
electronics rack.
17. The monitoring system of claim 16, wherein the heat exchange
assembly comprises an air-to-air heat exchanger, and wherein the
control unit dynamically determines effectiveness of the air-to-air
heat exchanger employing a difference between the sensed coolant
temperatures at the coolant outlet and coolant inlet of the heat
exchanger (.DELTA.T.sub.sense), and a difference between the sensed
air temperature at the air outlet side of the electronics rack and
the sensed coolant temperature at the coolant inlet of the heat
exchanger (.DELTA.T.sub.inlet), and employs effectiveness of the
heat exchanger in determining the airflow rate through the
electronics rack.
18. The monitoring system of claim 17, wherein effectiveness
(.epsilon.) of the heat exchanger is defined as:
.DELTA..times..times..DELTA..times..times. ##EQU00002## and wherein
the control unit determines coolant flow rate through the heat
exchanger, and hence the electronics rack, as:
CFM=e.sup.[(.epsilon.-A)/B] where A and B are constants obtained by
pre-calibrating the heat exchanger for the determined coolant rate
through the heat exchanger.
19. The monitoring system of claim 16, wherein the heat exchange
assembly comprises an air-to-liquid heat exchanger, and wherein the
monitoring system further comprises a coolant pressure sensor at
the coolant inlet to the heat exchanger, and a coolant pressure
sensor at the coolant outlet of the heat exchanger, and a
temperature sensor at an air outlet side of the heat exchanger
(T.sub.ro2), and wherein the at least one temperature sensor
disposed at the air outlet side of the electronics rack is disposed
between the electronics rack and the heat exchanger and thus senses
air temperature at an air inlet side of the heat exchanger
(T.sub.ro), and wherein the control unit is further coupled to the
pressure sensors and to the air temperature sensor at the air
outlet side of the heat exchanger, and further determines capacity
rate (C.sub.r) of air flowing through the heat exchanger employing
coolant mass flow rate through the heat exchanger, and a difference
between the sensed coolant temperatures at the coolant outlet and
coolant inlet of the heat exchanger (.DELTA.T.sub.sense), and a
difference between the sensed air temperatures at the air outlet
and air inlet sides of the heat exchanger (.DELTA.T.sub.RDHX), and
employs capacity rate (C.sub.r) of air flowing through the heat
exchanger in determining the power being consumed at the
electronics rack.
20. The monitoring system of claim 19, further comprising at least
one temperature sensor disposed at an air inlet side of the
electronics rack, and the control unit determines power being
consumed at the electronics rack by employing the determined
capacity rate (C.sub.r) of airflow through the heat exchanger and a
difference between the sensed air temperature at the air outlet
side of the electronics rack and the sensed air temperature at the
air inlet side of the electronics rack (.DELTA.T.sub.rack), and
wherein the control unit further comprises determining airflow rate
through the electronics rack as:
CFM=2118.9.times.C.sub.r/(C.sub.p.times..rho.) where C.sub.p is the
coolant specific heat and .rho. is the coolant mass density, and
wherein the control unit further determines power being consumed at
the electronics rack as: rack
power=C.sub.r.times..DELTA.T.sub.rack.
Description
TECHNICAL FIELD
The present invention relates in general to computer room or data
center monitoring and management, and more particularly, to
monitoring methods and systems for ascertaining airflow rate
through and power consumption of an electronics rack to facilitate
management of cooling within a data center containing one or more
electronics racks.
BACKGROUND OF THE INVENTION
The power dissipation of integrated circuit chips, and the modules
containing the chips, continues to increase in order to achieve
increases in processor performance. This trend poses a cooling
challenge at both the module and system level. Increased airflow
rates are needed to effectively cool high power modules and to
limit the temperature of air that is exhausted into the computer
center.
In many large server applications, processors along with their
associated electronics (e.g., memory, disk drives, power supplies,
etc.) are packaged in removable drawer configurations stacked
within a rack or frame. In other cases, the electronics may be in
fixed locations within the rack or frame. Typically, the components
are cooled by air moving in parallel airflow paths, usually
front-to-back, impelled by one or more air moving devices (e.g.,
fans or blowers). In some cases it may be possible to handle
increased power dissipation within a single drawer by providing
greater airflow, through the use of a more powerful air moving
device or by increasing the rotational speed (i.e., RPMs) of an
existing air moving device. However, this approach is becoming
problematic at the rack level in the context of a computer
installation (i.e., a data center).
The sensible heat load carried by the air exiting the rack is
stressing the ability of the room air-conditioning to effectively
handle the load. This is especially true for large installations
with "server farms" or large banks of electronics racks close
together. In such installations not only will the room
air-conditioning be challenged, but the situation may also result
in recirculation problems with some fraction of the "hot" air
exiting one rack unit being drawn into the air inlet of the same
rack or a nearby rack. This recirculating flow is often extremely
complex in nature, and can lead to significantly higher rack inlet
temperatures than expected. This increase in cooling air
temperature may result in components exceeding their allowable
operating temperature and in a reduction in long term reliability
of the components.
SUMMARY OF THE INVENTION
The shortcomings of the prior art are overcome and additional
advantages are provided in one aspect through the provision of a
method of monitoring an electronics rack which includes a heat
exchanger disposed at an air outlet side thereof. The method
includes: sensing air temperature at the air outlet side of the
electronics rack; sensing coolant temperature at a coolant inlet to
the heat exchanger and coolant temperature at a coolant outlet of
the heat exchanger; determining at least one of airflow rate
through the electronics rack or power being consumed by the
electronics rack, the determining employing the sensed air
temperature at the air outlet side of the electronics rack and the
sensed coolant temperatures at the coolant inlet and outlet of the
heat exchanger, wherein a known percentage of air egressing from
the electronics rack passes through the heat exchanger; and
outputting the determined airflow rate through the electronics rack
and/or power being consumed at the electronics rack.
In a further aspect, a monitoring system for an electronics rack is
presented. The monitoring system includes: a heat exchange assembly
disposed at an air outlet side of the electronics rack; at least
one temperature sensor disposed at the air outlet side of the
electronics rack between the electronics rack and the heat exchange
assembly; a coolant temperature sensor disposed to sense coolant
temperature at the inlet to the heat exchanger and a coolant
temperature sensor disposed to sense coolant temperature at the
outlet of the heat exchanger; and a control unit coupled to the
temperature sensors for obtaining sensed temperature values and for
employing the sensed temperature values in dynamically determining
and outputting at least one of airflow rate through the electronics
rack and power being consumed at the electronics rack.
Further, additional features and advantages are realized through
the techniques of the present invention. Other embodiments and
aspects of the invention are described in detail herein and are
considered a part of the claimed invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The subject matter which is regarded as the invention is
particularly pointed out and distinctly claimed in the claims at
the conclusion of the specification. The foregoing and other
objects, features, and advantages of the invention are apparent
from the following detailed description taken in conjunction with
the accompanying drawings in which:
FIG. 1 depicts one embodiment of a data center room layout
illustrating a plurality of electronics racks to be monitored, in
accordance with one or more aspects of the present invention;
FIG. 2A is an isometric view of one electronics rack of the
plurality of electronics racks depicted in FIG. 1, in accordance
with an aspect of the present invention;
FIG. 2B is a cross-sectional elevational view of the electronics
rack of FIG. 2A, taken along line 2B-2B, in accordance with an
aspect of the present invention;
FIG. 2C is a cross-sectional elevational view of the electronics
rack of FIG. 2A, taken along line 2C-2C, in accordance with an
aspect of the present invention;
FIG. 3A is an isometric view of the electronics rack of FIG. 2A,
modified with monitoring components as depicted in FIGS. 3B &
3C, in accordance with an aspect of the present invention;
FIG. 3B is a cross-sectional elevational view of the electronics
rack with monitoring components of FIG. 3A, taken along line 3B-3B,
in accordance with an aspect of the present invention;
FIG. 3C is a cross-sectional elevational view of the electronics
rack with monitoring components of FIG. 3A, taken along line 3C-3C,
in accordance with an aspect of the present invention;
FIG. 4A is an elevational view of one detailed embodiment of a heat
exchange assembly employable in the monitoring methods and systems
described herein, in accordance with an aspect of the present
invention;
FIG. 4B is a side elevational view of the heat exchanger embodiment
of FIG. 4A, in accordance with an aspect of the present
invention;
FIG. 5A is a partial isometric view of an alternate heat exchange
assembly embodiment, in accordance with an aspect of the present
invention;
FIG. 5B is a partial isometric view of another alternate heat
exchange assembly embodiment, in accordance with an aspect of the
present invention;
FIG. 6 is a plot of heat exchanger effectiveness versus rack
airflow rate (CFM) through the heat exchanger for various
calibrated coolant flow rates through the heat exchanger, in
accordance with an aspect of the present invention;
FIG. 7 is a flowchart of one embodiment of processing for
determining airflow rate through and power consumption of an
electronics rack using the monitoring components of FIGS. 3B &
3C, in accordance with an aspect of the present invention;
FIG. 8A is an isometric view of the electronics rack of FIG. 2A,
modified with an alternate embodiment of monitoring components as
depicted in FIGS. 8B & 8C, in accordance with an aspect of the
present invention;
FIG. 8B is a cross-sectional elevational view of the electronics
rack with monitoring components of FIG. 8A, taken along line 8B-8B,
in accordance with an aspect of the present invention;
FIG. 8C is a cross-sectional elevational view of the electronics
rack with monitoring components of FIG. 8A, taken along line 8C-8C,
in accordance with an aspect of the present invention; and
FIG. 9 is a flowchart of one embodiment of processing for
determining airflow rate through and power consumption of an
electronics rack using the monitoring components of FIGS. 8B &
8C, in accordance with an aspect of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
As used herein, the terms "electronics rack", "rack-mounted
electronic equipment", and "rack unit" are used interchangeably,
and unless otherwise specified include any housing, frame, rack,
compartment, blade server system, etc., having one or more heat
generating components of a computer system or electronics system,
and may be, for example, a stand alone computer processor having
high, mid or low end processing capability. In one embodiment, an
electronics rack may comprise multiple electronics subsystems, each
having one or more heat generating components disposed therein
requiring cooling. "Electronics subsystem" refers to any
sub-housing, blade, book, drawer, node, compartment, etc., having
one or more heat generating electronic components disposed therein.
Each electronics subsystem of an electronics rack may be movable or
fixed relative to the electronics rack, with the electronics
drawers of a multi-drawer rack unit and blades of a blade center
system being two examples of subsystems of an electronics rack to
be cooled.
As used herein, "air-to-liquid heat exchange assembly" means any
heat exchange mechanism characterized as described herein through
which liquid coolant can circulate; and includes, one or more
discrete air-to-liquid heat exchangers coupled either in series or
in parallel. An air-to-liquid heat exchanger may comprise, for
example, one or more coolant flow paths, formed of thermally
conductive tubing (such as copper or other tubing) in thermal
communication with a plurality of air-cooled cooling fins. Size,
configuration and construction of the air-to-liquid heat exchange
assembly and/or air-to-liquid heat exchanger thereof can vary
without departing from the scope of the invention disclosed herein.
An "air-to-air heat exchange assembly" may comprise, for example,
any heat exchange mechanism characterized as described herein
through which cooled air can circulate; and includes one or more
discrete air-to-air heat exchangers coupled either in-series or
in-parallel. An air-to-air heat exchanger may comprise, for
example, one or more coolant flow paths, formed of thermally
conductive tubing (such as copper or other tubing) in thermal
communication with a plurality of air-cooled cooling fins. Size,
configuration and construction of the air-to-air heat exchanger can
vary without departing from the scope of the invention disclosed
herein. Further, "data center" refers to a computer installation
containing one or more electronics racks to be cooled. As a
specific example, a data center may include one or more rows of
rack-mounted computing units, such as server units.
One example of liquid coolant employed in an air-to-liquid heat
exchange assembly is water. However, the concepts disclosed herein
are readily adapted to use with other types of liquid coolant. For
example, one or more of the liquid coolants may comprise a brine, a
fluorocarbon liquid, a liquid metal, or other similar coolant, or
refrigerant, while still maintaining the advantages and unique
features of the present invention. Further, as explained further
below, in various embodiments, an air-to-air heat exchange assembly
may be employed wherein the coolant is cooled air forced or drawn
through the heat exchanger. Thus, unless otherwise specified, the
word "coolant" is used herein as either a gaseous coolant or a
liquid coolant.
Reference is made below to the drawings, which are not drawn to
scale for reasons of understanding, wherein the same reference
numbers used throughout different figures designate the same or
similar components.
FIG. 1 depicts one embodiment of a raised floor, data center room
layout 100 typical in the prior art. In this layout, multiple
electronics racks 110 are disposed in one or more rows. A computer
installation such as depicted in FIG. 1 may house several hundred,
or even several thousand, microprocessors. In the arrangement of
FIG. 1, chilled air enters the computer room via floor vents 160
from a supply air plenum 145 defined between the raised floor 140
and a base or sub-floor 165 of the room. Cooled air is taken in
through louvered front covers 121 at air inlet sides of the
electronics racks 110 and expelled through the back covers 131 (at
the air outlet sides) of the electronics racks. Each electronics
rack 110 may have an air moving device (e.g., fan or blower) to
provide forced inlet-to-outlet airflow to cool the electronics
within the subsystem(s) of the rack. The supply air plenum 145
provides conditioned and cooled air to the air inlet sides of the
electronics racks via perforated floor tiles 160 disposed in a
"cold" aisle of the computer installation. The conditioned and
cooled air is supplied to plenum 145 by one or more
air-conditioning units 150, also disposed within the computer
installation 100. Room air is taken into each air-conditioning unit
150 near an upper portion thereof. This room air comprises in part
exhausted air from the "hot" aisles of the computer installation
defined, for example, by opposing air outlet sides of the
electronics racks 110.
FIGS. 2A-2C depict one embodiment of a single electronics rack of
the multiple electronics racks depicted in FIG. 1. Referring
collectively to these drawings, electronics rack 110 includes an
air inlet side 120 covered by front cover 121 and an air outlet
side 130 covered by back cover 131. In this embodiment, electronics
rack 110 comprises a plurality of horizontally-disposed electronics
subsystems 200, such as a plurality of server nodes. As shown,
airflow is front-to-back via perforated openings in the front cover
121 and back cover 131 of the electronics rack. As air flows
through the electronics rack, it passes over the server nodes 200,
which in this embodiment, are positioned horizontally via rails 210
within electronics rack 110. The front and rear covers at the air
inlet and air outlet sides of the electronics rack may include
slanted corners, as illustrated in FIG. 2A, to facilitate pivoted
opening of the front and back covers.
Limiting factors for cooling an air-cooled data center such as
depicted in FIG. 1 are related to the maximum chilled airflow rate
that can be supplied from a single perforated tile, the maximum
cooling capabilities of each air-conditioning unit, and the hot air
recirculation phenomenon that is common in these systems. Hot air
recirculation occurs when the total airflow rate of supplied
chilled air in front of an electronics rack is less than the total
rack airflow rate, leading to the hot exhaust air from one
electronics rack being drawn into the intake of the same or another
electronics rack, thus potentially resulting in unacceptably high
rack inlet temperatures. As noted, this can impact reliability and
performance of the electronics in the rack, and also lead to device
failure in extreme cases.
Data center thermal problems may be addressed using one of at least
two approaches. Specifically, by a human operator, with some degree
of trial and error, making changes in the layout of perforated
tiles, server racks, air-conditioning units, and room geometry
(e.g., ceiling, walls, partitions, ducts, type of tiles), or by
changing the operating point of the air-conditioning units (e.g.,
air or liquid flow rate, set point temperatures, etc.).
Alternatively, computer-based techniques may be employed to model
the data center, simulate several "what if?" scenarios, and then
derive a plan for making actual changes to improve cooling within
the computing clusters. For both approaches, it would be
significant to know the rack airflow rate, as well as the rack
power consumed, so that air-conditioning unit infrastructure can be
sized and located to provide the requisite cooling, which is not
too little (i.e., a reliability problem) or too much (i.e., an
energy inefficiency problem). This data is almost never provided in
a transparent manner to the room air-conditioning operator. In most
real world situations, the rack airflow rate and rack power are
unknown quantities that have to be guessed at based on nameplate
data, which can lead to significant errors in the thermal design of
the data center. Thus, disclosed hereinbelow are various methods
and systems to readily determine rack airflow rate and rack power
consumption.
Two embodiments are described hereinbelow, one employing an
air-to-air heat exchange assembly, and the other an air-to-liquid
heat exchange assembly. In both embodiments, air temperature is
sensed at the air outlet side of the electronics rack, and coolant
inlet temperature and coolant outlet temperature to the heat
exchange assembly are sensed. These temperature values are then
employed in dynamically determining at least one of airflow rate
through the electronics rack or power being consumed at the
electronics rack, wherein it is assumed that a known percentage of
air egressing from the electronics rack passes through the heat
exchange assembly (e.g., 100%). The monitoring method and system
described hereinbelow then output the determined airflow rate
and/or power consumption of the electronics rack, for example, by
displaying the airflow rate and/or power consumption to an operator
of the data center. In the embodiments described herein, a single
electronics rack is discussed, however, those skilled in the art
will understand that the concepts described are readily adapted to
a plurality of electronics racks disposed within a data center
configuration. For example, each electronics rack within the data
center may separately provide the temperature values required to
ascertain the airflow rate through and power consumption of that
electronics rack to a centralized monitoring unit for the data
center.
FIGS. 3A-3C illustrate one embodiment of an electronics rack with
monitoring components, in accordance with an aspect of the
invention disclosed herein. Electronics rack 110 again includes an
air inlet side 120 and an air outlet side 130, with respective
covers 121, 131 which have openings to facilitate airflow from the
air inlet side to the air outlet side of the electronics rack.
Added in this embodiment are a plurality of rack inlet temperature
sensors 300 T.sub.1, T.sub.2, T.sub.3, T.sub.4, T.sub.5, T.sub.6
& T.sub.7, and a plurality of rack exhaust temperature sensors
310 T.sub.8, T.sub.9, T.sub.10, T.sub.11, T.sub.12, T.sub.13 &
T.sub.14, which are electrically coupled to a control unit 320 via
data cables 315.
In this embodiment, an air-to-air heat exchange assembly 330 is
located at the air outlet side of electronics rack 110 with the
rack exhaust temperature sensors 310 being disposed on the air
inlet side of air-to-air heat exchanger 330, as illustrated. Heat
exchange assembly 330 may be preexisting in association with the
electronics rack or may be disposed at the air outlet side of the
electronics rack expressly for facilitating monitoring of airflow
rate through and/or power consumed by the electronics rack, in
accordance with the concepts disclosed herein. Coolant passing
through this heat exchange assembly, which in one embodiment is
cooled air, passes through at least one channel extending through
the heat exchange assembly. This at least one channel is referred
to herein as the "sense loop". Heat exchange assembly 330 includes
a coolant inlet 331 and a coolant outlet 332, with coolant outlet
332 being coupled to an air moving device 335 for drawing air
through the sense loop of the heat exchange assembly. Fan 335 is
shown disposed, by way of example only, at the coolant outlet 332
of heat exchange assembly 330. In addition, an inlet temperature
sensor 341 is disposed to sense coolant inlet temperature and an
outlet temperature sensor 342 is disposed to sense coolant outlet
temperature. Temperature sensors 341, 342 are also coupled via data
cables 315 to control unit 320, which as noted above, employs the
temperature readings in determining the airflow rate through and
power consumed by the electronics rack, as explained further
hereinbelow.
The sense loop of the heat exchange assembly is calibrated in the
laboratory so that for a certain RPM of fan 335, a known airflow
rate through the sense loop is obtained. This data, along with the
various sensed temperature values, is sent to control unit 320,
which includes logic for automatically determining the rack airflow
rate and power consumption. In one example, the determined rack
airflow rate and/or power being consumed may be displayed
automatically in a transparent manner at the control unit itself,
or may be otherwise output for use in managing the data center
cooling. As used herein, the word "output" includes display,
printing or electronically saving of the determined information,
for example, at the control unit or at a central monitoring unit
for the data center.
FIGS. 4A & 4B depict one embodiment of an a heat exchange
assembly 330 employable in monitoring rack airflow rate and power
consumption, as described herein. Referring to both figures
collectively, heat exchange assembly 330 is shown to include an
inlet plenum 400 in fluid communication with coolant inlet 331 and
an outlet plenum 410 in fluid communication with coolant outlet
332. Disposed between inlet plenum 400 and outlet plenum 410 are a
plurality of thermally conductive tubes 420, for example, six metal
tubes, such as copper tubes, in the illustrated embodiment. A heat
exchange assembly support frame 430 may also be provided to provide
rigidity to the heat exchange assembly and facilitate mounting of
the heat exchange assembly to the electronics rack within the
outlet cover at the air outlet side of the electronics rack. In the
embodiment of FIGS. 3A-3C, air-moving device 335 is employed to
establish a suction flow through a sense loop comprising coolant
inlet 331, inlet plenum 400, tubes 420, outlet plenum 410 and
coolant outlet 332. If desired, the coolant inlet port may be
disposed above a floor tile with a cutout to draw cool air directly
from the underfloor plenum, and thereby maximize the temperature
difference between the two air streams, that is, the cooled air
passing through the sense loop compared with the heated air
exhausting out the air outlet side of the electronics rack and
passing across the heat exchange assembly.
FIGS. 5A & 5B depict two alternate embodiments of a portion of
a heat exchange assembly which may be employed in defining a sense
loop for use in determining rack airflow rate and rack power
consumption, as described herein. In FIG. 5A, a sense loop air tube
500 is shown surrounded by a plurality of fins 510 extending
therefrom. Using this embodiment, air egressing from the
electronics rack (not illustrated) passes through the plurality of
fins 510 and around the sense loop air tube 500, resulting in the
transfer of heat to the coolant passing through the heat exchanger
sense loop defined in part by the sense loop air tube 500. FIG. 5A
is a conventional fin and tube heat exchanger section, while FIG.
5B illustrates a plate fin and flat tube compact heat exchanger
design, which may alternately be employed in the heat exchange
assembly disposed at the air outlet side of the electronics rack.
In FIG. 5B, the sense loop air tube 520 section comprises a
plurality of flat tubes interconnected by thermally conductive fins
530. As in the above-described embodiments, air egressing from the
air outlet side of the electronics rack transfers heat to the
coolant passing through the sense loop of the heat exchange
assembly.
FIG. 6 illustrates examples of the underlying physics employed by
the processes described herein. As noted, FIGS. 3A-3C illustrate an
air-to-air heat exchange assembly embodiment in which air egressing
from the electronics rack flows past the metal tubes, thus heating
the cooler air flowing within the tubes of the heat exchange
assembly. One thermal performance metric of a heat exchanger is its
effectiveness (.epsilon.), which is defined as the ratio of the
heat the exchanger is capable of transferring from one stream to
another, to the theoretical maximum heat exchange possible for some
given inlet temperature values. Effectiveness is a measure of how
well a given heat exchanger design performs under certain input
conditions. In practical terms, effectiveness can be calculated
using the ratio of two temperature difference terms. The numerator
is the temperature rise in the fluid (e.g., air) stream with the
smaller of the two capacity rates (i.e., within the sense loop).
The capacity rate is calculated as the product of the volumetric
airflow rate, the specific heat, and the density. The denominator
is the temperature difference between the inlet temperature of the
hot air stream (i.e., electronics rack exhaust), and the inlet of
the cold stream (i.e., the inlet coolant to the sense loop). FIG. 6
depicts various curves illustrating variation of heat exchanger
effectiveness with the total electronics rack flow rate, and the
sense loop airflow rate. A representative heat exchange design was
employed to produce the illustrated plots of typical heat exchanger
behavior. Three different plots are illustrated, one each for 60,
80 & 100 CFM sense loop airflow (determined, for example, from
the RPMs of the fan drawing air through the sense loop).
Plots of effectiveness versus electronics rack flow rate can be
readily generated in a laboratory prior to shipment of an
electronics rack with a heat exchange assembly as described herein.
Thus, in the field, using the various temperature sensors, and
knowledge of the sense loop airflow rate to fan RPM relationship,
heat exchanger effectiveness can be determined. Then, using a known
relationship (described below) between the effectiveness and the
rack flow rate, real-time rack airflow rate can be determined. A
representative curve fit expression allowing the calculation of the
rack airflow rate when effectiveness is known is shown in FIG. 6 in
the box labeled "Field Data Reduction".
FIG. 7 illustrates a flowchart of one embodiment for determining
rack airflow rate and power consumption employing the monitoring
components of FIGS. 3A-3C. Rack airflow rate and power consumption
determination 700 begins with the control unit (or centralized
monitoring unit) obtaining data from the various temperature
sensors 710. Specifically, rack inlet temperature sensors T.sub.1 .
. . T.sub.7 provide air temperature values for air entering the air
inlet side of the electronics rack, rack outlet temperature sensors
T.sub.8 . . . T.sub.14 provide air temperature values for air
egressing from the electronics rack, inlet temperature sensor
T.sub.si provides temperature of air entering the coolant inlet of
the sense loop of the heat exchange assembly, and temperature
sensor T.sub.so provides temperature of air exiting the coolant
outlet of the sense loop.
Next, the control unit calculates various derived parameters 720.
In this example, the average rack inlet temperature T.sub.ri is
calculated and the average rack outlet air temperature T.sub.ro is
calculated by simple averaging of the respective sensed temperature
values. More representative temperature values are achieved by this
averaging of the inlet air temperatures and averaging of the outlet
air temperatures. In an alternate embodiment, more or less
temperature sensors may be employed to obtain the air inlet and air
outlet temperature values. Area weighted factors could also be
employed if a particular sensor is used to represent a larger area
than another sensor. In a like manner, in cases where the flow is
known to be spatially non-uniform, flow weight factors could also
be employed to calculate the average air temperature.
The control display next determines various thermal parameters 730,
including .DELTA.T.sub.inlet, .DELTA.T.sub.sense, and
.DELTA.T.sub.rack. These thermal parameters, which are defined in
Table 1 below, are then employed in determining effectiveness of
the heat exchange assembly, and hence airflow rate through the
electronics rack and power consumed by the electronics rack 740.
The equations employed in determining efficiency, airflow rate
through the electronics rack, capacity rate of the air passing over
the heat exchange assembly and rack power are described below.
After determining rack airflow rate and power consumed, the results
may be output by the control unit or forwarded to a monitoring unit
(not shown) for centralized output 750. The control unit then waits
a defined time interval t.sub.1 before returning to obtain a new
set of temperature sensor readings 760, and automatically repeating
the transparent determination of rack airflow rate and power
consumption.
The variables and equations employed in the flowchart of FIG. 7 are
defined as follows:
TABLE-US-00001 TABLE 1 Variable/Equation Definition T.sub.1,
T.sub.2, T.sub.3, T.sub.4, T.sub.5, T.sub.6, T.sub.7 Air
temperature values measured via corresponding sensors located at
the air inlet side of the rack. T.sub.8, T.sub.9, T.sub.10,
T.sub.11, T.sub.12, T.sub.13, T.sub.14 Air temperature values
measured via corresponding sensors located at the air outlet side
of the rack. T.sub.si Air temperature measured via sensor located
at the coolant inlet of the sense loop T.sub.so Air temperature
measured via sensor located at the coolant outlet of the sense loop
T.sub.ri Average air temperatures calculated via averaging of data
from sensors at rack inlet. T.sub.ro Average air temperatures
calculated via averaging of data from sensors at rack exhaust.
.DELTA.T.sub.inlet Temperature difference between the average rack
exhaust air (T.sub.ro) & the inlet sense loop air temperature
(T.sub.si). .DELTA.T.sub.sense Temperature difference between the
inlet and exit sense loop air (T.sub.so - T.sub.si).
.DELTA.T.sub.rack Temperature difference between air at server
inlet (T.sub.ri) & air at server exhaust (T.sub.ro). .epsilon.
Effectiveness of the heat exchanger. CFM Rack airflow in Cubic Feet
per Minute. C.sub.r Capacity rate of the rack airflow which
characterizes the air's ability to carry heat away. It is the
product of the volumetric flow rate, the mass density, and the mass
specific heat. Rack Power Power consumed by the rack (or other
electronic equipment) located in the rack. T.sub.ri = [T.sub.1 +
T.sub.2 + T.sub.3 + T.sub.4 + T.sub.5 + T.sub.6 + T.sub.7]/7 Simple
spatial temperature averaging. T.sub.ro = [T.sub.8 + T.sub.9 +
T.sub.10 + T.sub.11 + T.sub.12 + T.sub.13 + T.sub.14]/7 Simple
spatial temperature averaging. .DELTA.T.sub.inlet = T.sub.ro -
T.sub.si This is the temperature difference that drives the
exchange of the heat between the two fluid streams (both air in
this case). This is commonly known as the "heat exchanger inlet
temperature difference". This is the difference in the temperature
of two fluid streams entering the heat exchanger. In this case,
those temperatures are the exhaust rack air temperature and the
inlet sense loop air temperature. .DELTA.T.sub.sense = T.sub.so -
T.sub.si This is the temperature difference between the sense loop
air at the inlet and at the exit. .rho. Mass density of air in
kg/m.sup.3. C.sub.p Specific heat of air in J/kg-K. A, B Constants
determined via fitting data using regression analysis.
.DELTA.T.sub.rack = T.sub.ro - T.sub.ri This is the temperature
difference between the rack air at the inlet and at the exit
thereof. .epsilon. = .DELTA.T.sub.sense/.DELTA.T.sub.inlet This is
the heat exchanger effectiveness. It represents the ratio of the
actual heat exchanged between the fluid streams versus the maximum
possible heat that could be exchanged. This is a characteristic of
the heat exchanger and is determined by its physical design, the
thermophysical properties of the materials that are used in its
construction, the thermophysical properties of the fluids that flow
through it, and the mass flow rates of the fluids that flow through
the device. A simple derivation yields the equation used herein to
calculate effectiveness.
More particularly, the heat (q) exchanged between the two air
streams via the heat exchange device is given by:
q=.epsilon..times.C.sub.min.times..DELTA.T.sub.inlet (1)
Where .epsilon. is the heat exchanger effectiveness, and
.DELTA.T.sub.inlet is the inlet temperature difference that is
driving the heat exchange between the two fluid streams (e.g., air)
that are flowing through the heat exchanger. In the embodiment
shown in FIGS. 3A-3C, .DELTA.T.sub.inlet is equal to
(T.sub.ro-T.sub.si). Also, in equation (1) above, the parameter
C.sub.min is the minimum of the two fluid stream capacity rates.
Since the flow through the sense loop (.about.100 CFM) is an order
of magnitude lower than that through the rack (>1000 CFM), the
sense loop air flow capacity rate, C.sub.s, is the minimum capacity
rate. This gives:
q=.epsilon..times.C.sub.s.times.(T.sub.ro-T.sub.si) (2)
The heat transferred to the sense loop air stream will increase the
air temperature of this sense loop air, and can be calculated
using: q=C.sub.s.times.(T.sub.so-T.sub.si) (3)
Combining equations (2) and (3) to solve for .epsilon., yields,
.epsilon.=.DELTA.T.sub.sense/.DELTA.T.sub.inlet
This effectiveness is a function of the rack flow rate and can be
calibrated in the laboratory to yield the following function,
CFM=e.sup.[(.epsilon.+A)/B] Where A and B are constants fitted
using regression analysis.
The rack flow in SI units which are m.sup.3/s is obtained by
dividing CFM by 2118.9 (CFM/(meter.sup.3/sec)), and the rack
airflow capacity rate (C.sub.r) in SI units is calculated by
multiplying the volumetric flow rate (m.sup.3/s) by the air mass
density (kg/m.sup.3) and the air specific heat (J/kg-K),
C.sub.r=(CFM/2118.9).times.C.sub.p.times..rho.
Now that the rack air flow capacity rate is known, the heat added
to the air stream by the heat generating components in the rack can
be calculated using knowledge of the difference in air temperature
between the inlet air (T.sub.ri) and the exhaust air (T.sub.ro),
Rack
Power=C.sub.r.times..DELTA.T.sub.rack=C.sub.r.times.(T.sub.ro-T.sub.ri)
FIGS. 8A-8C illustrate an alternate embodiment of an electronics
rack with monitoring components, in accordance with an aspect of
the invention disclosed herein. In this embodiment, electronics
rack 110 again includes an air inlet side 120 and an air outlet
side 130, with respective covers 121, 131, which have openings to
facilitate airflow from the air inlet side to the air outlet side
of the electronics rack. The embodiment further includes a
plurality of rack inlet temperature sensors 800 T.sub.1, T.sub.2,
T.sub.3, T.sub.4, T.sub.6 & T.sub.7, and a plurality of rack
outlet temperature sensors 810 T.sub.8, T.sub.9, T.sub.10,
T.sub.11, T.sub.12, T.sub.13 & T.sub.14, which are electrically
coupled to a control unit 820 via data cables 815.
In this embodiment, an air-to-liquid heat exchange assembly 830 is
located at the air outlet side of electronics rack 110, with the
rack exhaust temperature sensors 810 being disposed on the air
inlet side of the air-to-liquid heat exchange assembly 830, as
illustrated. Heat exchange assembly 830 may be preexisting in
association with the electronics rack, for example, to reduce the
heat load on the room air-conditioning units within the data
center, or may be disposed at the air outlet side of the
electronics rack expressly for facilitating monitoring of airflow
rate and/or power being consumed by the electronics rack, in
accordance with the concepts disclosed herein.
In the embodiment of FIGS. 8A-8C, coolant passing through the heat
exchange assembly is a liquid, and in one example is water. This
liquid coolant passes through at least one channel within the heat
exchange assembly, again referred to herein as the "sense loop". By
way of example, the heat exchange assembly could again comprise a
configuration similar to that depicted in FIGS. 4A-5B. Heat
exchange assembly 830 includes a coolant inlet 831, and coolant
outlet 832, with the coolant inlet 831 having associated therewith
a coolant inlet temperature sensor 833, and a coolant inlet
pressure sensor 834, and the coolant outlet 832 having associated
therewith a coolant outlet temperature sensor 835, and a coolant
outlet pressure sensor 836. Coolant inlet and outlet temperature
sensors 833 & 835 measure inlet and outlet temperature,
respectively, of the liquid coolant passing through the sense loop
of the heat exchange assembly, while coolant inlet and outlet
pressure sensors 834 & 836 monitor inlet and outlet pressure,
respectively, of coolant flowing into and out of the sense loop.
These coolant temperature and pressure sensors are also coupled via
data cables 815 to control unit 820. The monitoring components
further include, in this embodiment, a plurality of heat exchanger
outlet temperature sensors 840 T.sub.15, T.sub.16, T.sub.17,
T.sub.18, T.sub.19, T.sub.20 & T.sub.21 disposed at the air
exhaust side of the heat exchanger between the heat exchanger and
the outlet cover 131.
FIG. 9 illustrates a flowchart of one embodiment for determining
rack airflow rate and rack power consumption employing the
monitoring components of FIGS. 8A-8C. Rack airflow rate and power
consumption determination 900 begins with the control unit (or
centralized monitoring unit) obtaining data for various temperature
and pressure sensors 910. Specifically, rack inlet temperature
sensors T.sub.1 . . . T.sub.7 provide air temperature values for
air entering the air inlet side of the electronics rack, outlet
temperature sensors T.sub.8 . . . T.sub.14 provide air temperature
values for air egressing from the electronics rack (and entering
the heat exchange assembly), temperature sensors T.sub.15 . . .
T.sub.21 provide air temperature values for air egressing from the
heat exchange assembly, coolant inlet temperature sensor T.sub.si
provides temperature of the liquid coolant at the inlet to the
sense loop of the heat exchange assembly, coolant outlet
temperature sensor T.sub.so provides temperature of the coolant at
the coolant outlet of the sense loop, inlet pressure sensor
P.sub.si provides coolant pressure at the coolant inlet to the
sense loop, and pressure sensor P.sub.so provides coolant pressure
at the outlet of the sense loop.
Next, the control unit calculates various thermal parameters 920.
In this example, the average rack inlet temperature T.sub.ri is
calculated and the average rack outlet temperature T.sub.ro is
calculated by simple averaging of the respective sensed temperature
values. Similarly, the average heat exchanger outlet air
temperature T.sub.ro2 is calculated by simple averaging of the
temperature sensors T.sub.15 . . . T.sub.21. Further, the coolant
pressure drop (.DELTA.P) through the heat exchange assembly is
calculated by determining the difference between the coolant
pressure at the coolant inlet to the sense loop minus the coolant
pressure at the coolant outlet of the sense loop.
The control unit next determines various derived parameters 930,
including .DELTA.T.sub.inlet, .DELTA.T.sub.sense,
.DELTA.T.sub.RDHX, .DELTA.T.sub.rack, m.sub.s, and C.sub.s. These
parameters, which are defined in Table 2 below, are then employed
in determining a capacity rate for airflow through the heat
exchange assembly, airflow rate through the heat exchange assembly,
and hence through the electronics rack, and rack power being
consumed at the electronics rack 940. The equations employed in
determining capacity rate, airflow rate through the electronics
rack and rack power are similar to those described above in
connection with the processing of FIG. 7. After determining rack
airflow rate and power consumed, the results may be displayed by
the control unit or otherwise output, or forwarded to a centralized
monitoring unit of the data center for centralized display or other
output 950. Processing then waits a defined time interval t.sub.1
before automatically returning to obtain a new set of temperature
and pressure sensor readings 960, and repeating the determination
of rack airflow rate and/or power consumption.
The variables and equations employed in the flowchart of FIG. 9 are
defined in Table 1 above, and Table 2 below.
TABLE-US-00002 TABLE 2 Variable/Equation Definition T.sub.15,
T.sub.16, T.sub.17, T.sub.18, T.sub.19, T.sub.20, T.sub.21 Air
temperature measured via sensors located at the rear of the heat
exchanger (RDHX). P.sub.si Water pressure measured via sensor
located at the coolant inlet of the sense loop. P.sub.so Water
pressure measured via sensor located at the coolant outlet of the
sense loop. .DELTA.T.sub.RDHX Temperature difference between air at
RDHX inlet (T.sub.ro) and air at RDHX exhaust (T.sub.ro2).
T.sub.ro2 Spatially averaged air temperature at the rear of the
rear door heat exchanger (RDHX). .DELTA.P Water pressure drop
across the rear door heat exchanger between inlet/outlet sense
points. m.sub.s Water mass flow rate through the rear door heat
exchanger. C.sub.s Water capacity rate through the rear door heat
exchanger. C.sub.pw Water specific heat which can be determined via
commonly available technical sources. .rho..sub.w Water mass
density which can be determined via commonly available technical
sources. T.sub.ro2 = [T.sub.15 + T.sub.16 + T.sub.17 + T.sub.18 +
T.sub.19 + T.sub.20 + T.sub.21]/7 Simple spatial temperature
averaging. .DELTA.T.sub.RDHX = T.sub.ro - T.sub.ro2 This is the
temperature rise in the air as it flows through the rear door heat
exchanger. Using the knowledge of the heat that is transferred to
the water in the RDHX, the air capacity rate can be calculated, and
thus also the air volumetric airflow rate and consequently, the
rack power that is being rejected to the air. .DELTA.P = P.sub.so -
P.sub.si This is the temperature difference between the sense loop
air at the inlet and at the outlet. m.sub.s = [.DELTA.P/D].sup.G
This is the mass flow rate of the water flowing through the sense
loop which is also the rear door heat exchanger. The constants D
and G can be determined via laboratory testing or calibration and
can then be used in conjunction with the .DELTA.P to determine the
mass flow rate. C.sub.s = m.sub.s .times. C.sub.pw .times.
.rho..sub.w This is the capacity rate of the water flowing through
the RDHX. C.sub.s .times. .DELTA.T.sub.sense This is the heat
gained by the water stream in the rear door heat exchanger. C.sub.r
= (C.sub.s .times. .DELTA.T.sub.sense/.DELTA.T.sub.RDHX) This is
the air capacity rate that is flowing through the rear door heat
exchanger. Since the heat lost by the air is gained by the water,
this is derived from a simple energy balance where the heat gained
and lost are equated. CFM = 2118.9 .times. C.sub.r/(C.sub.p .times.
.rho.) When the C.sub.r is divided by the product of the air
specific heat and the air density, it yields the air volumetric air
flow rate in SI units (m.sup.3/s). Multiplying this value by 2118.9
yields the air volumetric airflow rate in cubic feet per minute
(CFM).
The detailed description presented above is discussed in terms of
procedures which can be executed on a computer, a network or a
cluster of computers. These procedural descriptions and
representations are used by those skilled in the art to most
effectively convey the substance of their work to others skilled in
the art. They may be implemented in hardware or software, or a
combination of the two.
A procedure is here, and generally, conceived to be a sequence of
steps leading to a desired result. These steps are those requiring
physical manipulations of physical quantities. Usually, though not
necessarily, these quantities take the form of electrical or
magnetic signals capable of being stored, transferred, combined,
compared, and otherwise manipulated. It proves convenient at times,
principally for reasons of common usage, to refer to these signals
as bits, values, elements, symbols, characters, terms, numbers,
objects, attributes or the like. It should be noted, however, that
all of these and similar terms are to be associated with the
appropriate physical quantities and are merely convenient labels
applied to these quantities.
Further, the manipulations performed are often referred to in
terms, such as closing or opening, which are commonly associated
with manual operations performed by a human operator. No such
intervention of a human operator is necessary in the operations
described herein which form part of the present invention; the
operations may be implemented as automatic machine operations.
Useful machines for performing the operations of the present
invention include general purpose digital computers or similar
devices.
Aspects of the invention are preferably implemented in a high level
procedural or object-oriented programming language to communicate
with a computer. However, the inventive aspects can be implemented
in assembly or machine language, if desired. In any case, the
language may be a compiled or interpreted language.
The invention may be implemented as a mechanism or a computer
program product comprising a recording medium. Such a mechanism or
computer program product may include, but is not limited to
CD-ROMs, diskettes, tapes, hard drives, computer RAM or ROM and/or
the electronic, magnetic, optical, biological or other similar
embodiment of the program. Indeed, the mechanism or computer
program product may include any solid or fluid transmission medium,
magnetic or optical, or the like, for storing or transmitting
signals readable by a machine for controlling the operation of a
general or special purpose programmable computer according to the
method of the invention and/or to structure its components in
accordance with a system of the invention.
Aspects of the invention may be implemented in a system. A system
may comprise a computer that includes a processor and a memory
device and optionally, a storage device, an output device such as a
video display and/or an input device such as a keyboard or computer
mouse. Moreover, a system may comprise an interconnected network of
computers. Computers may equally be in stand-alone form (such as
the traditional desktop personal computer) or integrated into
another environment (such as a partially clustered computing
environment). The system may be specially constructed for the
required purposes to perform, for example, the method steps of the
invention or it may comprise one or more general purpose computers
as selectively activated or reconfigured by a computer program in
accordance with the teachings herein stored in the computer(s). The
procedures presented herein are not inherently related to a
particular computing environment. The required structure for a
variety of these systems will appear from the description
given.
The capabilities of one or more aspects of the present invention
can be implemented in software, firmware, hardware or some
combination thereof.
One or more aspects of the present invention can be included in an
article of manufacture (e.g., one or more computer program
products) having, for instance, computer usable media. The media
has therein, for instance, computer readable program code means or
logic (e.g., instructions, code, commands, etc.) to provide and
facilitate the capabilities of the present invention. The article
of manufacture can be included as a part of a computer system or
sold separately.
Additionally, at least one program storage device readable by a
machine embodying at least one program of instructions executable
by the machine to perform the capabilities of the present invention
can be provided.
The flow diagrams depicted herein are just examples. There may be
many variations to these diagrams or the steps (or operations)
described therein without departing from the spirit of the
invention. For instance, the steps may be performed in a differing
order, or steps may be added, deleted or modified. All of these
variations are considered a part of the claimed invention.
Although preferred embodiments have been depicted and described in
detail herein, it will be apparent to those skilled in the relevant
art that various modifications, additions, substitutions and the
like can be made without departing from the spirit of the invention
and these are therefore considered to be within the scope of the
invention as defined in the following claims.
* * * * *